Understanding Earth Chapter 20: COASTLINES AND OCEAN BASINS Grotzinger • Jordan Understanding Earth Sixth Edition Chapter 20: COASTLINES AND OCEAN BASINS © 2011 by W. H. Freeman and Company

Coastlines and Ocean Basins Chapter 20 Coastlines and Ocean Basins

About Coastlines and Ocean Basins Coastal processes are the interaction of the climate system and the solar system. Waves and tides are key processes at the coastline. The ocean basin contains features like mountains, valleys, and volcanoes.

Lecture Outline How ocean basins differ from continents 2. Coastal processes 3. The shaping of shorelines 4. Continental margins 5. Topography of the deep sea floor 6. Ocean sedimentation

How Ocean Basins Differ from Continents ● Lack of fragmentation processes ● slow chemical weathering ● Limited tectonic activity ● mid-ocean ridges and subduction zones ● Oceans dominated by volcanism and sedimentation

● Wave motion – key to shoreline dynamics 2. Coastal Processes ● Wave motion – key to shoreline dynamics ● Wind waves: depends on wind speed, duration, and distance

Coastal Processes: Straight Sandy Beach Pea Island, North Carolina

Coastal Processes: Rocky Coastline Mount Desert Island, Maine

Coastal Processes: Wave Erosion Effects Port Campbell, Australia

Coastal Processes: Reef and Beach southern Florida

● period for successive waves 2. Coastal Processes ● To describe a wave ● wavelength ● wave height ● period for successive waves

● The velocity of a wave (V) ● V = L x T ● L = wavelength ● T = period 2. Coastal Processes ● The velocity of a wave (V) ● V = L x T ● L = wavelength ● T = period

2. Coastal Processes: Wave Motion Near Shore

2. Coastal Processes: Wave Motion Near Shore

2. Coastal Processes: Wave Motion Near Shore

2. Coastal Processes: Wave Motion Near Shore

2. Coastal Processes: Wave Motion Near Shore

● waves break (collapse) as they approach the shore 2. Coastal Processes ● The surf zone ● nearshore area ● waves break (collapse) as they approach the shore ● swash and backwash on shore

● wave crests bend as they approach the shore 2. Coastal Processes ● Wave refraction ● wave crests bend as they approach the shore ● waves break (collapse) as they approach the shore ● swash and backwash on shore

● Longshore currents (parallel to shore) 2. Coastal Processes ● Longshore currents (parallel to shore) ● caused by wave approach at an angle to the shore ● zig-zag path of swash and backwash occurs at the shore ● Rip currents (perpendicular to shore)

● The tides: gravitational origin ● solar tides 2. Coastal Processes ● The tides: gravitational origin ● solar tides ● lunar tides: spring and neap

● Earth-Moon-Sun alignment ● shoreline configuration 2. Coastal Processes ● The height of tides ● Earth-Moon-Sun alignment ● shoreline configuration ● tidal surges with storms

Bulging Water of the Tides 2. Coastal Processes: Bulging Water of the Tides

2. Coastal Processes: Spring Tides

2. Coastal Processes: Neap Tides

● Tidal currents ● flood tidal current ● ebb tidal current 2. Coastal Processes ● Tidal currents ● flood tidal current ● ebb tidal current

● Hurricanes and storm surges ● cyclonic storms with winds 2. Coastal Processes ● Hurricanes and storm surges ● cyclonic storms with winds of 260+ km/hr (160+ mi/hr) ● ahead of the storm: dome of sea water floods coastal areas

Coastal Processes: Hurricane Katrina, August 2005

Coastal Processes: Storm Surge Effects New Orleans, Louisiana

Coastal Processes: Storm Surge Effects Hurricane Katrina – August 2005

Coastal Processes: Storm Surge Effects

● Hurricanes and their intensity ● Saffir-Simpson scale 2. Coastal Processes ● Hurricanes and their intensity ● Saffir-Simpson scale ● counter-clockwise in northern hemisphere

Coastal Processes: Hurricanes

Thought questions for this chapter After a period of calm along a section of the Gulf Coast of North America, a severe storm with high tides passes over the shore and up the Mississippi Valley. Describe the state of the surf zone before the storm, during it, and after the storm has passed. What would happened to inland rivers?

● foreshore (surf zone, tidal flat, and swash zone) ● offshore 3. The Shaping of Shorelines ● Structure of beaches ● backshore ● foreshore (surf zone, tidal flat, and swash zone) ● offshore

3. The Shaping of Shorelines: The Structure of Beaches

● Sand budget of the beach ● incessant movement 3. The Shaping of Shorelines ● Sand budget of the beach ● incessant movement ● input and output (erosion and sedimentation) ● changing conditions lead to growth or shrinkage

● Shoreline erosion and deposition ● uplift / subsidence 3. The Shaping of Shorelines ● Shoreline erosion and deposition ● uplift / subsidence ● nature of rocks or sediments ● changes in sea level ● average storm wave heights ● heights of tides

● Erosional coastal forms ● sea cliffs and wave-cut terraces 3. The Shaping of Shorelines ● Erosional coastal forms ● sea cliffs and wave-cut terraces ● Depositional coastal forms ● barrier islands and spits

Shorelines: Four Wave-Cut Terraces California

Shorelines: Sand Spit and Barrier Islands Cape Cod, Massachusetts

● Sea-level change due to warming ● melting of ice caps 3. The Shaping of Shorelines ● Sea-level change due to warming ● melting of ice caps ● expansion of water in oceans ● Effects on beaches: net erosion and loss of the beach

Thought questions for this chapter Why would you want to know the timing of high tide if you wanted to observe a wave-cut terrace? In a 100-year period, the southern tip of a long, narrow, north-south beach has become extended by about 200 m to the south by natural processes. What shoreline processes could have caused this extension?

Thought questions for this chapter You are studying a sequence of sedimentary rocks and discover that the beds near the base are shallow marine sandstones and mudstones. Above these beds is an unconformity, overlying which are nonmarine sandstones. Above this group of beds is another unconformity; overlying it are marine beds similar to those at the base. What could account for this sequence?

● Types of continental margin ● passive ● active 4. Continental Margins ● Types of continental margin ● passive ● active ● Components of continental margins ● shorelines ● shelves, slopes, and rises

4. Continental Margins: Passive Submarine canyons Deep-sea fan Coastal plain Abyssal plain Continental shelf Continental slope Continental crust Oceanic crust Continental rise Mantle

Active (Marianas Type) 4. Continental Margins: Active (Marianas Type) Island arc Forearc basin Trench Accretionary wedge

4. Continental Margins: Active (Andean Type) Continental volcanic belt Offshore trench Continental crust Oceanic crust Mantle Accretionary wedge

● low sloping offshore area ● economically important 4. Continental Margins ● Continental shelves ● low sloping offshore area ● economically important ● Continental slope and rise ● canyons and submarine fans ● turbidity flows of sediment

Continental Margins: Sand Flow in Canyon California

Continental Margins: Submarine Canyons SHELF SLOPE RISE offshore New England

● How we know about the deep ● Deep Sea Drilling Project 5. Topography of the Deep Sea Floor ● How we know about the deep ● Deep Sea Drilling Project ● Ocean Drilling Program ● ship-towed instruments ● deep-diving submarines ● satellite charting of seafloor

5. Topography of the Deep Sea Floor

5. Topography of the Deep Sea Floor

● volcanic tracks of hot spots ● deep sea trenches ● island arcs 5. Topography of the Deep Sea Floor ● Important features ● mid-ocean ridges ● volcanic tracks of hot spots ● deep sea trenches ● island arcs ● continental margins

● continental slope and rise ● submarine canyons 5. Topography of the Deep Sea Floor ● Oceanic profiles ● continental shelf ● continental slope and rise ● submarine canyons ● abyssal hills and plains ● seamounts, plateaus, and island chains ● mid-ocean ridges

5. Topography of the Deep Sea Floor: The Atlantic Ocean Profile

The Deep Ocean: The Atlantic Mid-Ocean Ridge, Southwest of the Azores

5. Topography of the Deep Sea Floor: The Pacific Ocean Profile

Thought questions for this chapter What are the chief differences between the Atlantic and Pacific oceans with regard to topography, tectonics, volcanism, and other seafloor processes? There is very little sediment on the floor of the central valley of the Mid-Atlantic Ridge. Why is this so? How might plate tectonics account for the contrast between the broad continental shelf off the eastern coast of North America and the narrow, almost nonexistent shelf off the western coast?

Thought questions for this chapter A major corporation hires you to determine whether New York City’s garbage can be dumped at sea within 100 km offshore. What kinds of places would you explore, and what are your concerns?

● Continental shelf sedimentation ● clastics from land ● biochemical 6. Ocean Sedimentation ● Continental shelf sedimentation ● clastics from land ● biochemical ● Deep-sea sedimentation ● pelagic sediments and foraminiferal oozes ● windblown silt and clay ● siliceous oozes (silica plankton)

Oceanic Sediments: Ooze Made of Planktonic Organisms

Chemical Weathering and Depth 6. Ocean Sedimentation: Chemical Weathering and Depth

Thought questions for this chapter A plateau rising from the deep-sea floor to within 2000 m of the surface is mantled with foraminiferal ooze, whereas the deep seafloor below the plateau, about 5000 m deep, is covered with reddish brown clay. How can you account for this difference?

Key terms and concepts Abyssal plain Active margin Barrier island Abyssal hill Abyssal plain Active margin Barrier island Beach Carbonate compensation depth Continental margin Continental rise Continental shelf Continental slope Foraminiferal ooze Guyot Hurricane Longshore current Passive margin

Key terms and concepts Seamount Shoreline Siliceous ooze Spit Pelagic sediment Seamount Shoreline Siliceous ooze Spit Storm surge Tidal flat Tide Turbidity current Wave-cut terrace